A communication network interconnects nodes that have an interface to a communication medium used by the network. The nodes can be network devices that communicate between one another, for example, as well as devices that facilitate that communication such as hubs, routers, and bridges. The communication medium can be the physical elements providing a link between the nodes, such as twisted-wire cables, coaxial cable, and power lines. Communication over a network can occur over multiple layers each having a protocol designed for that layer. For example, communication between two network devices having a direct physical link might use one protocol layer, while communication between two network devices separated by other nodes such as routers and bridges might use another protocol layer.